Compliance is of extreme importance in assessing quality of life since lost data never can be retrieved. In order to assess this issue in various studies, a cross-sectional study in cured cancer patients, three prospective trials and a normative study were explored. In the cross-sectional study 82 per cent of the patients completed the questionnaires after one reminder. More females than males answered the questionnaires. The compliance rate varied from 99 per cent to 62 per cent in the prospective studies depending upon time after inclusion. It seems that compliance decreases during follow up, primarily because of disease progression. In one of the prospective studies low compliance rate (approximately 30 per cent) was found in the questionnaire assessing religious issues. In the normative study 68 per cent of the population completed the questionnaire. No gender differences were found, but younger males and elderly women were poor compliers. In conclusion, our data support that most patients complete quality of life questionnaires. It seems that patients with inferior education, reduced physical function and with progressive/terminal disease are low compliers. Introduction of the first quality of life questionnaires to the patients is of great importance. Detailed information about the study should be given and the importance of completing the questionnaires should be underlined.